This invention relates to an accelerometer or an acceleration detection-type sensor device, suitable for use in automobiles, ships, airplanes, and other moving bodies, for detection of acceleration in an inertial space. More specifically, this invention relates to an extremely small accelerometer or acceleration detection-type sensor device, of a form in which a spherical sensor part is supported buoyantly by an electrostatic supporting force.
An electrostatic gyro having a spherical gyro rotor and an electrostatic accelerometer are disclosed in Japanese Patent Application No. 3-118652, filed May 23, 1991 (Japanese Patent Laid-open No. 4-346021). This electrostatic gyro and electrostatic accelerometer comprises a spherical gyro rotor, and an electrostatic levitation startup device which levitates and holds the gyro rotor by means of electrostatic forces.
In general, active methods employing servo circuits, and passive methods employing resonance circuits, are known as methods to levitate and hold in a fixed position a gyro rotor or sensor part by means of electrostatic forces. In this example of the background art, a levitation method employing a resonance circuit is used.
In Japanese Patent Application No. 6-136074, filed Jun. 17, 1994 (Japanese Patent Laid-open No. 07-071965), the applicants of which are the present applicants, an electrostatic gyro device having a disc-shape gyro rotor is disclosed. In this example of the background art, a levitation method employing a servo circuit is used.
In the electrostatic gyros having spherical gyro rotors and electrostatic accelerometers of the background art, plate-shape electrodes were used. Hence the gap between the spherical gyro rotor and the electrodes was not fixed, and consequently there was the defect that the capacitance of the capacitor formed by the gyro rotor and the electrodes was small.
A restraining control system using a resonance circuit has a defect that various errors occur in the path from the power supply to the gyro rotor. Such errors include the occurrence of stray capacitances accompanying larger wiring and coils.
On the other hand, levitation methods employing servo circuits are used in electrostatic gyro devices having disc-shape gyro rotors; however, they have not been used in spherical sensor-type measurement devices having spherical sensor parts.
In light of these points, an object of this invention is to provide a spherical sensor-type measurement device or accelerometer in which the electrodes are formed in spherical shape, and the gap between the electrodes and the spherical mass part or the spherical sensor part is fixed.
In light of these points, an object of this invention is to provide an accelerometer capable of controlling the spherical sensor part by means of an active constraining control system.
In light of these points, an object of this invention is to provide a spherical sensor-type measurement device having an active constraining control system, as opposed to conventional passive constraining control systems.
The accelerometer of this invention comprises a spherical mass part of single-crystal or polycrystalline silicon, levitated by an electrostatic supporting force, and a plurality of electrodes positioned symmetrically so as to surround the spherical mass part, and having spherical inner surfaces.
According to this invention, an accelerometer comprises a plurality of the above electrostatic supporting electrodes and an electrode for displacement detection, positioned between the electrostatic supporting electrodes. Further, each of the above electrostatic supporting electrodes comprises a pair of electrode parts. The above electrostatic supporting electrodes comprise six electrostatic supporting electrodes, positioned along three mutually orthogonal axes.
According to this invention, in the accelerometer, the above electrostatic supporting electrodes and the above displacement detection electrode are mutually connected by a bridge positioned on the outside in the radial direction, formed in an integral structure. The above electrostatic supporting electrodes and the above displacement detection electrode are supported by a spherical shell-shape casing. On the outer surface of the above casing are arranged terminals connected to the above electrostatic supporting electrodes and the above displacement detection electrode, and an electrical wiring pattern connected to the terminals. The end parts of the above electrical wiring pattern form a prescribed array at a prescribed position on the outer surface of the above casing.
The accelerometer of this invention has:
a spherical mass part which is levitated by an electrostatic supporting force;
electrostatic supporting electrodes, positioned so as to surround the spherical mass part, and a displacement detection electrode, positioned between the electrostatic supporting electrodes;
a control operation part, which applies a control DC voltage to the above electrostatic supporting electrodes in order to generate the above electrostatic supporting force, and a displacement detection system, which applies to the above electrostatic supporting electrodes a displacement detection AC voltage, superposed on the above control DC voltage, which detects displacement detection current flowing in the above displacement detection electrode, and which generates a displacement detection voltage signal instructing a displacement of the above spherical mass part; and,
an acceleration output operation part which inputs the signal output by the above control operation part and operates the acceleration output; and in which
the above control operation part inputs the above displacement detection voltage signal output by the above displacement detection circuit, operates the correction amount for the above control DC voltage such that the displacement of the above spherical mass part becomes zero, and feeds this back to the above control DC voltage.
In the accelerometer of this invention, the above displacement detection AC voltage comprises AC voltage components having three mutually different displacement detection frequencies, corresponding to linear displacements in the three axis directions of the above spherical mass part. If the above displacement detection AC voltage applied to the above first electrostatic supporting electrode is ACX1, the above displacement detection AC voltage applied to the second electrostatic supporting electrode is ACXS, the above displacement detection AC voltage applied to the third electrostatic supporting electrode is ACY1, the above displacement detection AC voltage applied to the fourth electrostatic supporting electrode is ACY2, the above displacement detection AC voltage applied to the fifth electrostatic supporting electrode is ACZ1, and the above displacement detection AC voltage applied to the sixth electrostatic supporting electrode is ACZ2, then these are expressed by the following expressions.
ACX1=xe2x88x92EX=E0 cos(xcfx891t+xcex61)
ACx2=xe2x88x92EX=E0 cos(xcfx891t+xcex71)
ACy1=xe2x88x92Ey=E0 cos(xcfx892t+xcex61)
ACy2=xe2x88x92Ey=E0 cos(xcfx893t+xcex61)
ACz1=xe2x88x92Ez=E0 cos(xcfx891t+xcex61)
ACz2=xe2x88x92Ez=E0 cos(xcfx891t+xcex71)
Here xcfx891, xcfx892 and xcfx893 are displacement detection frequencies, and xcex61, xcex71, xcex62, xcex63, xcex73 are phase differences, which are related as follows.
xcex71=xcex61xc2x1180xc2x0
xcex72=xcex62xc2x1180xc2x0
xcex73=xcex63xc2x1180xc2x0
In the accelerometer of this invention, each of the above electrostatic supporting electrodes contains one pair of electrode parts; the above control DC voltages applied to this pair of electrode parts are of the same magnitude, but opposite polarity. The above control operation part has a displacement operation part which operates the displacement of the above spherical mass part, a PID operation part which operates the force to be applied to the above spherical mass part, and a control voltage operation part which operates the correction amount of the above control DC voltage. The above acceleration output operation part is configured to input the output signal of the above PID operation part and operates the acceleration output. The above spherical mass part comprises either single-crystal or polycrystalline silicon.
The spherical sensor-type measurement device of this invention has a spherical mass part which functions as an inertial force sensor; a spherical shell-shape enclosure part which surrounds the above spherical mass part; a displacement detection device which detects displacements of the above spherical mass part; and
electrodes positioned in the above enclosure part, and having spherical-shape inner surfaces.
In the spherical sensor-type measurement device of this invention, the above spherical mass part levitates by means of an electrostatic supporting force or magnetic force, and is configured such that a thin gap is formed between the spherical mass part and the above electrodes. The above electrodes include a plurality of electrostatic supporting electrodes, positioned symmetrically with respect to the above spherical mass part.